1. Technical Field
The present invention relates to imaging satellites and, more particularly, to a dual function satellite imaging and communication system using solid state mass data storage.
2. Discussion
Surveillance of the Earth from spaceborne platforms, or satellites, provides visual access to large portions of the Earth that are otherwise inaccessible due to terrain limitations or difficulties presented with the use of airborne platforms, such as air traffic congestion or aircraft fuel limitations. The broad perspective from spaceborne platforms is desirable because images that cover thousands of square miles and reveal features which are not recognizable from the Earth's surface or from airborne platforms may be observed.
Imaging of the Earth in the various wavelengths along the spectrum from visible to infra-red to radio frequency regions yields a wide range of information about the Earth's surface structure, physical properties, and environment. Satellite imaging may be accomplished by passive techniques, such as collecting the visible or infra-red radiation which is reflected or emitted by the objects that are being observed, or by active methods, such as radar, which generates radar pulses that are transmitted toward the Earth and received as they are reflected back into space.
For example, satellites such as LANDSAT, a multi-spectral imaging satellite which provides useful information about the surface of the Earth on a routine and regular basis, have imaging systems that collect image data through a focal plane assembly that are then transmitted through a separately gimballed antenna of a communication system to the Tracking Data Relay Satellite System (TDRSS). Finally, a ground processing facility on the Earth receives the data from the TDRSS and converts it into a useable form.
The separately gimballed antenna and/or aperture of the imaging and communication systems of prior imaging satellites significantly increases the cost and complexity of the imaging satellite spacecraft. Although previous satellite imaging systems have used tape recorders in lieu of communication cross-links in order to reduce the complexity of the satellite spacecraft, the reliability, data rate return and operational inflexibility of tape recorders have imposed other constraints on the utility of the satellite imaging system. Further, the prior imaging systems have been designed for relatively high duty cycle operation, such as 20%-30% (i.e. the satellite performs the imaging function and generates image data over 20%-30% of its orbit), and therefore require extensive solar cell systems to fulfill the imaging system's electrical power requirements. Ultimately, these factors have combined and have contributed to increasing the size and weight of the imaging satellite spacecraft, which is desired to be kept to a minimum, and have reduced the imaging satellite's reliability, which is of great concern because of the unique operating environment in which the satellite is placed.
Recent developments of low cost launch vehicle capabilities, such as those provided by Pegasus-type or Taurus-type launch vehicles, and the availability of solid state mass data storage devices, such as dynamic random-access computer memory, have presented the opportunity to develop a low cost imaging satellite which is capable of providing cost-efficient satellite imaging services for a wide variety of industrial or commercial applications, such as environmental monitoring services, meteorological services, and numerous other satellite imaging applications.